60 THE OAK. 



Successive sections prove that the vessels in the bun- 

 dle change in number i. e., there are fewer when pass- 

 ing from stem to leaf. A vessel may end in an inter- 

 pectinating, pointed, terminal cell; or it may branch, 

 as it were, dichotomously, owing to fusions with other 

 similar elements; or such a fusion may occur lower 

 down, the original vessel ending blindly. 



In the vicinity of the reticulated and first pitted ves- 

 sels, following on the spiral vessels, we find libriform 

 fibers, tracheids, wood-parenchyma, and secondary rays 

 of parenchyma ; the tracheids are especially in the neigh- 

 borhood of the vessels (see Fig. 14). 



The tracheids are long cells with gradually tapering 

 ends, and the walls rather thick but by no means obscur- 

 ing the lumen ; on the walls are numerous, usually elon- 

 gated, oblique or horizontal bordered pits. These pits 

 occur whether the next element is a tracheid, a vessel, 

 or fibers or cells of any kind (Fig. 16, tr). 



The length of the tracheids varies, and the diameter 

 is also variable. 



The libriform fibers are also long cells, but often 

 more pointed at the ends, and their very thick walls 

 almost obliterate the lumen (Fig. 16, /) ; their length is 

 about that of the tracheids, but slit-like, small, simple 

 pits are rare on their walls. In the wood of later years, 

 however, the lengths may be different. 



There are also elements which stand midway between 

 the true fibers and tracheids ; they occur in those parts 

 where masses of true fibers abut on the groups consist- 



